Electric circuit interrupter



Oct. 6, 1953 M. LAVERTY 2,654,815

ELECTRIC CIRCUIT INTERRUPTER Filed Dec. 27, 1948 & 27444 atorneg Patented Oct. 6, 1953 %654,815 ELECTRIC CIRCUIT INTERRUPTER Martin Lave'ty, West Hempstead, N. Y., assignor to Murray Manufacturig Corporation, Brooklyn, N. Y., a corporation of New York Application December 27, 1948, Serial No. 67,271

4 Claims.

The invention herein disclosed relates to an electric circuit interrupter of the kind in which relatively movable Contacts are separated to open or interrupt an electric circuit, such for example, as switches and circuit breakers. More particularly, and specifically, the invention relates to circuit interrupters of ncminal Capacity, that is rated around one hundred amperies and one hundred to two hundred and fifty volts, such as are commonly enclosed in a molded, thermoplastic case, and suitable for general use in factories, ofces and homes.

The primary object of the invention is to provide an arrangement of contacts and surrounding structure, in a circuit interrupter of the kind mentioned, which arrangement minimizes the arc produced at the contacts upon the separation of the Contacts to interrupt or open an electric circuit. .Another object of the invention is to provide such an arrangement in which, on interrupting an alternating current, the arc dies out as the current wave approaches zero. A further object of the invention is to provide an arrangement of the kind mentioned which acts to minimize the burning action of the Contacts, Another object of the invention is to provide such an arrangement wherein the air surrounding the arc is materially limited. An additional ob'ect of the invention is to provide such an arrangement in which the expanding gases generated in the formation of an arc are caused to travel a tortuous path in contact with heat-dissipating surfaces so that the gases and solid particles carried thereby are substantially cooled before the gases are vented to the surrounding air.

The foregoing obiects, and certain advantages that will hereinafter appear, are realized in the arrangements illustrated in the accompanying drawings and described in detail below, from which description a clear understanding of the invention may be had.

The drawings include:

Fig. 1 which is a sectional, side elevation of an arrangement of Contacts and surrounding structure embodying the invention;

Fig. 2 which is a transverse section of the same, taken on the line 2-2 of Fig. 1;

Fig. 3 which is an isometric View of one form of housing for the Contacts Fig. 4 which is a section of the housing of Fig. 3 taken on the line 4-4 of Fig. 3 and showing the housing within a case;

Fig. 5 which is an isometric View of another modified form of housing for the Contacts;

Fig. 5 which is a sectional, side elevation of the housing of Fig. 5, taken along the line 6-6 of Fig. 5;

Fig. 7 which is an isometric View of a shield for the housing of Fig. 5;

Fig. 8 which is an isometric view of the hous- :ing of Fig. 5 with the shielcl of Fig. 7 in place;

Fig. 9 which is a side elevation of another 2 form of an arrangement embodying the invention;

Fig. 10 which is a sectional, end elevation of the same taken on the line lo-lo of Fig. 9;

Fig. 11 which is an isometric, exploded view of the housing of Figs. 9 and 10.

While the principles orming the basis of this invention appear to have general utility in circuit interrupters of the kind mentioned, the invention is particularly and specifically useful in circuit interrupters, such for example, as switches and circuit breakers that are enclosed within a plastic case and which are of nominal, rated Capacity, such as circuit interrupters of general utility in factories, oflices and homes. In general, an arrangement embodying this invention includes two relatively movable Contacts and an enclosing or surrounding housing that forms an arc chamber. The relation of the contacts to each other, their size or mass, their relation to the enclosing housing and the structure and material of the enclosing housing are important factors in the arrangement of this invention. These several factors are so related as to minimize the arc produced upon the separation of the Contacts, and to minimize the destructive effects of any arc produced.

In accordance with the invention, the area and cross section or the mass of the Contacts, at the arcing surfaces, are greater than that required for normal heat dissipation and arc disposal; the separation of the Contacts, in interrupting a circuit, is limited to that distance which is necessary to insure a positive break regardless of any burning or lumping of the contact surfaces; the Contacts are surrounded, as closely as is mechanically feasible, with an arc chamber housing; and the housing, at least the side walls adjacent the side edges of the Contacts, consists of an insulatng material which does not lose its insulating characteristics after being subjected to numerous arcs, and, preferably, a material which assists in quenching any arc formed. Many and various arrangements may be designed to incorporate these principles and secure the advantages of the invention. However, after i numerous experiments and tests, the arrangements illustrated in the drawings have been found to be satisfactory in performance and economical to manufacture.

The arrangement illustrated in Figs. 1 and 2 of the drawing includes a stationary contact l and a eooperating movable contact 2 that is fixed on a movable arm 3. A housing, designated generally by the numeral 4 and forming an arc chamber, surrounds or encloses the Contacts l and 2. The housing 4 includes a bottom wall 5, an end wall S having a slot 'l therethrough, through which the movable arm 3 extends, a top wall 8, side walls 9 and ID, and an end wall ll, opposite the end wall 6. In this particular arrangement, the end wall H consists of a portion of a metallic strip, designated generally by the numeral [12, another portion of which constitutes the stationarycontactl The end wall' l l extends at right angles to the contact I, and at the opposite end thereof, another portion !3, extending at right angles to the wall H andparallel'tozthe contact l, forms a base for asolderlessconnector !4. The solderless Connector;l iisprovidedwith a pressure screw !5. In conneting'thewarrangement into an electric circuit,.a solid orstrande'd wire !8 is inserted between the -pressurescrew +5 and the portion !3 of the strip I2. The screw .I.5 is then tightened down and binds the wire*1'6`in intimate contact with the surface of the portion l3--of the strip* !2. 'Tl'e arm t isconneted'to -another wire in any suitable manner.

' Theyportionisof thes't'rip PZ is spaced from 'the top wall' 8 of the housing i *a' distance =such -`that` the engagingwall' i 'lufthe solderless connecter is spaced from ,the wall B to provide -a passage la therebetween. "The top wall -'*8 is 'foreshor-tened seas to provide'a vent' opening 1 9 between theen'd edge' thereof and the wall '-H. `This vent opening se :communicates `with*the passage I I'B.

The arrangement illustrate'd in Figs. "1 and and described above, is suitable for ineorpora'ting the-features which form the basis of this' invention "In designing an'arrangemento this kind, each of-the contacts -|--and`- 2^ are designedso that the area and "cross-section, ormass thereo'f, at *the Contacting -surfaces "or =aring s'urfaces 'is two or more times'the'area and cross 'seti'on or mass ofthat required for'the particular 'circuit interrupter, for normal-heat diss'ipation and arc disposal.

Contacts of electrical switches are considered to ihave suicient "contact-area; cross section `and mass, by the recognized "authority, the 'National Board of *Fire ,Underwritersjfthy 'do not rise in temperature, when &carrying full rated "load, more than thirty .degrees i( 30-) -c'entigrade -from an ambient "temperature 'of twenty five degrees (25) centigrade. Thecontacts'of circuit breakers 'are :considered satiSactOry, by the same authority, if their contacts *dohet-rise more than forty degrees ("40) centigrade from an ambient temperature ;of twenty five degrees (25 'centigrade when 'carrying fulrrated load. `=In accor`di ance with this invention, tlriecontacts 'are made so that the area'and cross *section or" mass is`two or "more times that specified -for the fu11 rated capacity of "the particularcircuit interrup'ter.

Experiments 'have shown that'with -such contacts, 'the arc formed -on `'short circuit tests is, on the average, -markedly-milder. The extra or greater 'metallic mass of the =contactsyacts fto r quickly conduct "the`heat away 'from the surfaces atwhich it'ori'ginates. ;An lectric arc 'in whih the Lheat is drawn out rapidly becomes 'less of an are, and 'this heat abstraction coupled with the arc reduction o'f'the falling alternating current wave tends ;to `insure "its disappearance *within one-half cycle, *and to 'prevent 'reestablishmert of the arc when the voltage rises in thereverse direction. i

In-addition,' movement "of the arm 3 is limited so that the separation`^20 of contacts l and-2,-in interrnpting ,a `circuit, is'limited to "that distance neeessaryto insure .a :positive break. `The limitation of ..theseparatingmovement of .the arm'3.may be-ieffectedby the length of `theslot 11 in'the `end wall 2, or byany other suitable means, Numerous experimentshaveushown that a separation of the contactingsurfaees of thecentacts i and Lindicated by the` arrowidesignated ;20 whichapproximateiy equals .the thicknessof the movable. c9n-` `stron-id surround or enclose the contacts l and 2,

as closely as is mechanically feasible. One rea- 'son for'this is to limit the amount oi air, or oxygen, available for any arc formed. In switches and circuit breakers :having fan Un'derwriter's rating upitooneshundredzamperes full'load, and

which are &required `'to sinterrupt a short circuit current up' tofive thousand amperes, the space between the side edge tof the'. movable iconta'ct 2 and the isi'de'wails *79 and |.0 of i the housing 4 is critical. .If 'this distance 'idesignated by 'the' numeral lzl, andindicatedbythe arrow, :is onethirtysecondof :an inchgthearc that-is formed on interrupting :a current aof five thousand amperes is at aaminimum. .As this space 2 l, 'between the side edges of theniovable'contact and the 'wals 9 'and iof "the housing, `is increased beyond "one -'thirtyz-second 'of :an `inch, -the are becomesfimoreesevere. :If'the'sdewalls-S and o are removed, the :arc :becomes extremely violent,

tothezpoint ofdexploding the plastic case normally used `with devices of ths character, and whose strength -is ample for &the higher arcs produced, 'withspaces between the edges of the contacts and theside walls '9 and HI :of `one-thirty-second of aninch. `The:sideedgesof-the stationarycontact l should, mreferably, .fit-or rather make a tight or *snug connection with the side wa1ls9 ;and I 0 of't-he housingain order to prevent burning of the side walls andsmolten metalaccumulation. .Contrary .to-the usual and accepted procedure in arcsuppression, this inventionminimizes magnetic blow-out action. Experiments and teste have -demonstr-ated vthat `a magnetic blow-out actionimay tend to increase the violence of an arc. .The magnetism forces the .arc away from the `contacts, .and .the .higher the current value onrancalternatingcurrent .wavethe more intense is the magneticaction. ..The net .result is that Whereas, with the .heavy contacts, .short breaks and othermeans described, the arc tends to die out with -the `current wave, with magnetic blowoutimeansthe arc oftenis -brokenhigh on the current wave and ;is (much more destructive in its burning action and fiame production. avoid this situation, the sta'tionary. contact I and the movable contact 2 `with 'its imovable arm .3 are carriedvin-.a straightline through opposite ends of the arcingchamber. Experiments have shownithatwhenthe stationarycontaet l is carried out through a ,side wallsuch ,as either the side walle. or JU), and cup along *the side wall of the arc chanber, the explolsive .action of any 1 are -produced is greatly intensifed.

The material radjacent 'the side edges of the 3 contacts "l and! spar'ticul'arly important, As

previously stated, it must *be an :electrical insulating ,substance which does ;not lose its insulating 'characteristics aft'erbeing subjected to numerous eres. *In-additionjit is highly desirable that the material adjacent the side edges of ,the contactsbe such that its reaction to the beat an are produces assists in minimzing or dissipating the :arc Eibre either vulcanized fibre or'horn .fibre possesses these chara'cteristics. hepmcess Qi xtingu shing'an:arcisa de-ionizing process and the arc is extinguished when there no longer are sufficient ions in the gap to maintain the are. Vulcanized fibre or horn fibre, under the heat of the arc, evolves neutral gases and water vapor which produce a turbulence in the arc stream, thereby accelerating the recombining of the ions with those of the opposite polarity to form neutral molecules. In addition, the gases evolved physically blow out the ionized arc stream if not completely enclosed, or when enclosed build up the pressure, thereby increasing the arcing potential in pressure-tight enclosures. Furthermore, the gases generated by fibre under an electric arc consist of approximately fifty percent carbon-monoxide, forty percent hydrogen and a five percent mixture of hydrocarbon gases in addition to the water vapor. The large percentage of carbon-monoxide generated shows that the carbon ormed on the surface by the arc actually combines with the oxygen in the cellulosic molecular structure of the fibre and escapes as a gas instead of being deposited on the surface in sufiicient quantities to cause tracking. Hence, fibre does not break down under the are until the material has been depleted of its oxidizing gases. Furthermore, by the action mentioned, the fibre adjaoent the Contacts assists in extinguishing any arc that is formed.

With the several factors, described above, for minimizing are production and cooling such arcs as are produced, it is possible to avoid the use of expensive arc-resisting contact tips, such as those made of tungsten-silver and other alloys. The burning of the Contacts is reduced to a point where Copper and brass combinations may safely be employed :for many Operations at full load, over load and short circuit values of current. Because of the light burning action, the tendency of the contacts to weld together under short circuit current is almost entirely eliminated. The Contacts tend to remain flat and the lumps and heads which result in contact welds are greatly reduced.

In the Construction shown in Figs. 1 and 2, and described above, the distance between the end edge of the contact 2 and the metallic end wall l i, indicated by the arrow and designated 22, is slightly more than the break distance 23 to insure that any are that may be formed will not hang-on," The metallic strip !2 is either copper or brass. When an arc is ormed, upon separation of the contacts to interrupt a heavy current, the molten particles flying out of the flaming arc stream tend to attach themselves to the surface of the metallic end wall I i as they strike it and are cooled thereby. This reduces the solid matter in the hot gases passing out through the vent !9 and the passage 13. In addition, the metal of the end wall ll and the passage iii dissipates the heat of the gases so that as the gases pass out of the passage ee, the temperature thereof is materially reduced.

In Fig. 3 of the drawing, there is illustrated a contact housing, or arc chamber, which, with the exception of one end wall is made up of sheets of fibre. This housing includes an end wall 22' having a slot therethrough for the arm 3 of the movable contact, a bottom Wall 25, a top wall 25 and side walls 2% and 2?. The several sheets forming these walls of the housing are assembled together through tongue and grcove joints. The end wall 22' is provided with several, four in number, openings 28 therethrough. The side walls 23 and 21 are likewise' provided with several openings, for example the four openings 29 in the side wall 21. The side wall 25 is provided with two tongues 30 and 3! which enter in the openings 28, and the side wall 21 is likewise provided with tongues 32 and 33 which enter in to openings 28 in the end wall 22'. The bottom wall 24 is provided with tongues 34 and 35 which enter into the lower openings 29 in the side wall 21. Similar tongues on the bottom wall 24 enter into similar openings in the wall 26. The top Wall 25 is provided with tongues 36 and 31 which enter into the upper pair of openings 29 in the wall 27. similar tongues on the opposite edge of the top wall 25 enter into like openings in the wall 25. No end wall opposite the end wall 22' is provided. As in the arrangement of Figs. 1 and 2 an extension of the stationary contact which will rest upon the bottom wall 24 may provide the end wall opposite to the end wall 22'.

The housing of Fig. 3 provides a simple and inexpensive housing or arc chamber for a switch or circuit breaker that is mounted within a plastic case. In the first place, it is made up of sheets of fibre that are readily stamped or cut to form. In addition, it may be readily inserted in a plastic case such for example as the case 38 (Fig. 4). In such an arrangement, the case 38 is provided with grooves 39 and 49 which receive the extended edges, side edges, of the end wall 22'. The housing makes a snug fit within the case 38 and is securely held together by the case.

It is not necessary that the entire housing for the contacts be made of fibre or other insulating material. In Figs. 5 and 6, there is disclosed an arc chamber that includes an end wall 4! which consists of fibre, and a metallic case designated generally by the numeral 42 which forms the remaining part of the chamber. The end wall 4l is provided with a slot 43 for the movable arm 3 of the movable contact 2. It is also provided with openings 44 and 45 and a groove 45 in the upper edge thereof.

The metallic casing 42 is desirably stamped from sheet metal and includes side walls 48 and '49, an end wall 50 and a top wall 5l. The side wall 48 is provided with a tab or tongue extension 52 which extends through the opening 44 in the end wall 4! and which is bent over to retain the side wall in contact with the end wall. A like tab 53 is formed on the side wall 41 and extends through the opening 45 in the end wall 4l. In addition, a tab 54 extends through the groove 46 in the upper edge of the end wall 4' and is bent over. These three tabs hold the stamping 42 to the fibre end wall 4I. With this Construction, the side walls 48 and 49 are provided with inner fibre linings 55 and 55. To secure the inner fibre lining 55 in place, the top wall 5! is provided with a slot 5'! through which a tongue or extension 58 of the lining extends. In addition, a slot 59 is provided between the side wall 48 and the end wall 58 through which another tongue 6!) of the lining 55 extends. In a like manner the lining 56 is secured to the side 49 of the metallic casing 42. Thus, in this arrangement there are fibre pieces adjacent the side edges of the Contacts.

With a contact housing or arc chamber such as that shown in Figs. 5 and 6, it is desirable to provide a shield that surrounds the metallic casing 42 to prevent carbonization of the plastc case in which the housing is mounted. Such a shield, El, is shown in Fig. 7. The shield SI, desirably, is a pressed fibre shield. Before mounting the are charnber 42 of Figs. 5 and 6 in a case,

such as the case 38, the shield e of Fig. 7 :is .applied to the housing `as shown in Fig. 8.

In Figs. 9 to 11, there is disclosed a very simple arrangement embodying this invention. The arrangement includes a metallic strip of bronze or copper, designated generally'by the numeral 62, and two fibre side plates 63 and 64. The strip '62 includes a central portion 6.5 which forms an end wall of the arc chamber. The central portion '65 has slots 66 and 61 in its side edges to receive tongues `68 and `69 of side pieces 63 and M respectively. The strip 152 also includes a portion 19 that extends at right angles to the portion 65' and constitutes the top of the arc chamber. The portion 'm 'has cut-away portions at 'H and 72 to receive extensions 13 and TM of the side pieces and 64. At the end of the central portion 65 opposite to that :end from which the portion Ti!) extends, there is a portion ;7:5 which also extends at right angles to the portion `65, and parallel to the portion '10. The cross section and area of the portion 15, which forms the stationary contact, is :that required `for 'normal clissipation of heat and :arc disposal. In order to obtain the mass desired, `or twice the area ,and cross section necessary for heat dissipation and arc disposal at the contact, 'the strip is bent 'back upon itself at '16 'to provide .a .portion 'il that is beneath, :and in intimate contact with the portion 15. The end edge of the stationary contact is notched at the corners, as at te and :119, to 'receive extensions ron the fibre :pieces 53 and 64, such as the extension 8.0 on the piece 63. The body of each of the fibre side walls `6.3 and 'is received :between the -portions 19 and 75. The side wall 363 is cut away .at 8! to provide a vent 82. in like maner the side wall `ti i is cut away at :83 to provide a similar vent. The portion ?a is provided with a 'threaded opening se to receive a terminal .screw :85. A movable contact 85 extends into the a-rc chamber with slight clearances. The whole assembly fits into a case (not shown) which holds the parts in assem'bled relation.

In addition to the oregoing arrangements, a fibre tube may be used :as .an arc 'housing for the contacts. Tubing made of fibre is a commercial product available on the 'open market. With its use, 'a simple and ec'onomical arc chamber may be provided, utilizing the principles herein disclosed.

'From the foregoing description 'of the principies of this invention and the detailed description of specific embodiments of the invention that are illustrated in the drawings, it will be apparent to those skilled in the art that by this invention there is provided, in a .circuit inter rup'ter, an arra-ngement o-f contacts and surrounding structure which arrangement minimizes the arc produced at the contacts upon the separation of the contacts to interrupt or open an electric circuit; which 'is such :that on interrupting an -alternating current any arc formed dies cut as the current :wave approaches zero; which acts to minimize the burning action of the contacts; which materially limits the air and oxygen surrounding the contacts and the arc acting therebetween; and which provides a tortuous path for the expanding gases generated in the formation of an arc which path is lined by heat dissipating surfaces so that the gases and molten meta particles carried thereby are substantially cooled 'before the gases .are vented to the surrounding air.

, It will :be cbvious, to those ;skilled in 'the art.,

that various changes may be made in the der' tails of the several embodments of the invention illustrated in the .drawings and specifically described above within the principle and scope of the invention as defined in the appended claims.

I claim:

1. In an electric circuit interrupter of the kind described, the combination .comprising a stationary contact, a 'movable contact positioned to cooperate with the stationary contact, said stationary contact constituting a portion of a strap of metal that includes a portion extending at an angle to the contact portion and another portion spaced from, extending in the .same direction as and substantially paral'lel to the contact portion, and fibre cooperating with said strap of metal to form a housing enclosing the contacts, the housing having openings ther-ethrough for the passage of gases generated by an arc formed between the contacts.

2. In an electric circuit interrupter of the kind described, the combination comprising a movable contact, a stationary .contact positioned to cooperate with the movable contact, said stationary contact constituting a portion of a meta-1 strip having a portion extending substantially at an angle to the contact portion and forming one wall of a housing for the contacts and another portion spaced from and substantially parallel to the contact portion and constituting another wall of the housing for the contacts and providing a connection for a line conductor, and fibre plates cooperating with said metal strip to form the housing for the contacts.

3. In a circuit interrupter of the kind described, the combination comprising a pair of relatively movable contacts, and a housing forming an arcing chamber for the contacts and including fibre side walls, a metal case for retaining the fibre walls in assembled relation, a fibre shield enclosing the metal case for minimizing the burning action of escaping arc-produced gases, and .a plastic case erclosing the circuit interrupter.

4. In a circuit interrupter of the kin-d described, the combination comprising a pair of relatively movable contacts, and a housing for the contacts consisting of a fibre, tube-like structure enclosing the contacts on four sides, and a metallic strip constituting one wall, one of the contacts entering the tube-like structure from one end thereof, and the other contact entering the tube-like structure from the opposite end thereof.

MARTIN LAVERTY.

References Gitcd -in the file of 'this patent UNITED STATES PATENTS Number Name Date 1,212,125 Burstyn Jan. 9, 1917 1,310,111 Ancotti et al July 15, 1919 1,798,854 Satchwell Mar. 31, 1931 2,293,70l Delmonte Aug. 25, 1942 2,294,801 Rawlins `Sept. l, 1942 2,363,606 Maseng Nov. '28, 1944 2,446,859 Traver Aug. 10, 1948 2,450,268 Bazley Sept. 28,194& 2,534,069 Schleicher Dec. 12, 1950 FORE'IGN PATENTS Number Country Date 317.71 `Great ,Britain u. Au 1% 9. 9 

